Study On Composition Design And Optimization Of La-Y-Ni Based A₂B₇-type Hydrogen Storage Alloy

The late-model La-Y-Ni based hydrogen storage alloy has attracted extensive attention of researchers at home and abroad because of its high energy density,low temperature resistance,easy preparation and environmental friendliness.In order to deeply study the relationship between the structure and properties of this alloy with special stacking structure,ternary（La,Y）₂Ni₇was prepared in this paper.The effects of different Y/La ratios on the structure and properties of（La,Y）₂Ni₇hydrogen storage alloy were studied by adjusting the proportion of La and Y elements in the alloy.Taking the ternary（La,Y）₂Ni₇hydrogen storage alloy with the best Y/La ratio as the object of element replacement and doping,the effects of different elements on the structure and properties of the alloy were studied by uniform experimental design and regression analysis.Finally,taking the alloy with the best cyclic performance after doping and replacement as the research object,the capacity attenuation mechanism of the alloy in electrochemical environment and solid/H₂reaction system was studied respectively.（1）The hydrogen storage alloy La_2-xY_4+xNi₂₁（x=0.1,0.2,0.3,0.4 and 0.6） was prepared by precursor powder sintering.It is found that the main phase of the alloy is 2H-Ce₂Ni₇and the secondary phase is 3R-Gd₂Co₇.Increasing the Y/La ratio is conducive to the formation of 3R-Gd₂Co₇phase.The electrochemical test results show that the maximum discharge capacity of the alloy electrode increases first and then decreases with the increase of Y/La.The maximum discharge capacity of the alloy is 282.2 m Ah·g^-1.The diffusion coefficient D₀of hydrogen in the alloy is the main factor affecting the dynamic properties of the alloy.The solid/H₂reaction test shows that the hydrogen absorption of high yttrium alloy is large,and the hydride of low yttrium alloy is more stable.（2）Take La_1.7Y_4.3Ni₂₁with the largest discharge capacity as the basic component,Mn and Al elements were used to partially replace Ni elements and additional Ti elements were added.Nine kinds of alloys were designed by uniform experimental design method.The results show that the addition of Ti will form Ti Ni₃phase with Ni on the B side,and too high Ti content will lead to La enrichment.There is interaction between Ti,Mn and Al.The hydrogen storage capacity and maximum discharge capacity of the alloy are greatly affected by Ti,and Ti has a negative effect.The cyclic stability of the alloy is negatively correlated with Ti.The alloys containing Ti,Mn and Al have better surface hydrogen dissociation activity.However,Mn and Al will hinder the diffusion of hydrogen atoms,and the hydrogen diffusion coefficient（D₀）is still the main factor affecting the alloy kinetics.（3）Preferably,the La_1.7Y_4.3Ni_19.4Mn_1.2Al_0.4alloy electrode appears pulverization and oxidation after 20 weeks of charge/discharge cycle.Compared with alloy La_1.7Y_4.3Ni₂₁,the electrochemical capacity retention of alloy La_1.7Y_4.3Ni_19.4Mn_1.2Al_0.4is improved after Mn and Y replace Ni on side B.In the first20 hydrogen absorption/desorption cycles,the decay rate of the alloy is the fastest,and then gradually slows down.The large volume deviation of 3R-Gd₂Co₇structure is the main reason for hydrogen induced amorphization after hydrogen absorption/desorption.